The present invention relates to a throwaway tip or insert adapted to be releasably mounted on a tool body for cutting tools, such as face cutters, and more particularly to a throwaway insert adapted to be mounted on the tool body so that either of the first (or upper) and second (or lower) major faces of the insert disposed in parallel and opposite to each other is located so as to constitute a flank which faces toward the external circumference of the tool body. The present invention further relates to a cutting tool with the above mentioned throwaway inserts attached thereto.
In the art of conventional cutting tools such as face cutters, a so-called vertical cutting edge type cutting tool is well known in which throwaway inserts are mounted on the tool body so that either of the upper and lower major faces of the insert, disposed in parallel and opposite to each other, is located so as to constitute a flank which faces toward the external circumference of the tool body.
An insert adapted for such a vertical cutting edge type cutting tool is disclosed in Japanese Unexamined Patent Publication JA-A-85790, as shown in FIGS. 34 to 36.
The disclosed insert has a rhombus-shaped flat plate configuration and comprises first and second rhombus-shaped major faces 1 and 2 disposed parallel and opposite to each other; a first pair of oppositely facing side faces 3a, 3a extending between the two opposite side margins of the first major face 1 and two opposite side margins of the second major face 2; and a remaining second pair of oppositely facing side faces 3b, 3b extending between remaining two side margins of the first major face 1 and remaining two side margins of the second major face 2. The major faces 1 and 2 have acute angle (.theta.) corners C1, C1 and obtuse angle corners C2, C2.
A first pair of major cutting edges 4, 4 and a second pair of major cutting edges 5, 5 are respectively constituted along each of the intersections of the first major face 1 with each of the first pair of side faces 3a, 3a, and the intersections of the second major face 2 with the second pair of side faces 3b, 3b. Rake faces 3a, 3a, 3b, 3b are respectively constituted on and represented by each of the side faces 3a, 3a, 3b, 3b adjoining said main cutting edge 4, 4, 5, 5. The rake faces 3a, 3a, 3b, 3b have an acute angle .phi. with the corresponding major face thereof.
Minor flanks 6, 6, 7, 7 are respectively formed along each of the intersections of the side faces 3b, 3b, 3a, 3a with the first and second major faces 1, 2 where the intersection does not constitute a major cutting edge. The minor flanks 6, 6, 7, 7 have one narrower end thereof intersecting with the rake faces 3a, 3a, 3b, 3b adjoining the major cutting edges 4, 4, 5, 5. Also, minor cutting edges 8, 8, 9, 9 are respectively constituted along the intersections of the minor flanks 6, 6, 7, 7 with the rake faces 3a, 3a, 3b, 3b.
As shown in FIGS. 37, 38, the insert 10 formed as above is mounted on a mounting seat 12 disposed on an external circumference at the front end of a tool body 11 having a substantially circular configuration. The insert 10 is selectively located on the mounting seat so that either of the first or second major faces 1, 2 is positioned to constitute a flank which faces toward the external circumference of the tool body 11, and one of the acute angle corner, C1, protrudes toward the front side of the tool body 11. In FIGS. 37, 38 the first or upper major face 1 is selected to be the flank, and the second or lower major face 2 is subsequently seated on the mounting seat 12, and one of the side faces 3a constitutes a rake face facing toward the direction of rotation of the tool body 11. After being so seated, the insert is clamped to the mounting seat 12 by means of a clamping screw. In operation, as the tool body 11 rotates around the axis of rotation thereof with the insert so mounted, one of the first pair of major cutting edges 4 adjoining the so selected rake face 3a and a corresponding one of the minor cutting edges 8, 8, 9, 9 proceed to the cutting of a work-to-be-machined (not shown). In the case shown in FIGS. 37, 38, the first major face 1 serving as the flank facing toward the external circumference of the tool body 11 has a relief angle .tau. with respect to the external circumference, and the rake face 3a facing toward the direction of rotation of the tool body 11 has a positive radial rake angle .beta. and a positive axial rake angle .alpha.. In turn, the side face 3b which adjoins the rake face 3a at the acute angle corner C1 has a positive relief angle .delta..
The insert 10 may be selected to be seated on the second major face contacting the mounting seat 12 but with the other of the first pair of major cutting edges 4 positioned for cutting by turning the insert 10 by 180 degrees. Furthermore, the insert 10 may be selected to be seated on the first major face 1 contacting the mounting seat 12, whereby either of the second major cutting edges 5, 5 is positioned for cutting. Consequently, the four major cutting edges 4, 4, 5, 5 and the four minor cutting edges 6, 6, 7, 7 may be subjected to the use for cutting by appropriately selecting the attitude of the insert 10.
The conventional insert described above has a disadvantage. With respect to the conventional insert, it is known that, increasing the axial rake angle .alpha. and the radial rake angle .beta. of the major cutting edges 4, 5 when mounting on the tool body 11 is an effective method to improve machineability by reducing the cutting resistance subjected to the major cutting edges 4, 5.
However, the conventional insert has the rake faces 3a, 3b thereof formed to have a single slant face of a constant plane angle .phi. with the first and second major faces from the acute, angle corner C1 to the obtuse angle corner C2. Accordingly, in order to increase the axial rake angle .alpha. of the major cutting edges 4, 5 as discussed above, the vertex angle .theta. of the acute angle corner, or the plane angle between the rake faces 3a and 3b must be decreased, thereby decreasing the strength of the cutting edge tip at the acute angle corner C1 and tending to cause a possible breaking in the edge. Increasing the radial rake angle .beta. also involves a decrease in the included angle of the major cutting edges 4, 5 which is identical to the plane angle .phi. discussed above, again causing a possible decrease in the cutting edge strength.
The conventional insert also has another disadvantage. The strength and rigidity of the major cutting edge of the conventional insert is often found to be insufficient for machining hard material such as die steel and material having welded sections since, as discussed above, the rake angle is kept at a constant positive angle of less than 90 degrees and, subsequently the included angle of the major cutting edge is relatively small.